1. Field of the Invention
This invention relates to an annular drilling hammer having an annular bore crown guided between an outer tube and an inner tube. An annular hammer piston periodically strikes the bore crown and has a piston member that is guided in a cylindrical chamber having control apertures which are connected fluidically to a reversing valve. The working medium is delivered to the reversing valve between an inner tube system and an outer tube system. After driving the hammer piston the medium is discharged from the drill between the outer tube and the bore crown. The bore crown is provided with flow channels leading from the rear shoulder through and to the front and/or central aperture of the bore crown. The flow of driving medium through these channels aids the entrainment of bored material, which then is carried out through the inner tube system. Preferred bore crown configurations are shown for preventing core building.
2. Description of the Prior Art
Prior art annular drilling or coring devices (U.S. Pat. No. 3,524,511 and U.S. Pat. No. 3,299,971) are designed with annular bore crowns which employ a helical motion to obtain the corings. The coring sample is pushed up into the hollow region within the drill rods as the drill penetrates. Such prior art devices have used a core lifter ring which is fitted at the crown of the device. When the drill rods are lifted at the end of the coring procedure, the core lifter ring holds the coring sample within the drill rods so that both may be removed from the hole at once. The core sample may then be removed from the drill rods for examination and geological testing.
In known annular drilling hammers or core drills, the drive mechanism for a deep hole hammer is effected by compressed air conducted between the inner tube rods and outer tube rods and fed to a reversing valve for the hammer piston. The outgoing air from the hammer piston drive system flows out of the annular gap between the bore crown and the outer tube and finally escapes for the major part between the outer tube and the bore wall. The soil, rock or other boring material dislodged by the rotary percussion effect of the bore crown is flushed up between the outer tube and the bore hole wall by the escaping working fluid. The core, which cannot be flushed up because of its substantial weight, remains inside the bore crown or the inner tube.
The problem with such prior art devices is that the walls of the bore hole may collapse. This may block or strongly throttle the discharge of the driving and rinsing medium, which can then flow back only through the very limited space inside the drill rods. That interior space is mostly occupied by the drill core. In case of a collapse at the bore hole bottom, a complete blockage may result in which the working fluid can no longer be discharged at all. The resultant counterpressure built up in the annular drilling hammer then can put the hammer out of operation.
Other deep hole hammers (U.S. Pat. No. 2,823,013) conduct the exhaust air directly through the bore crown to permit an out-flow directly at the bore hole bottom. Rinsing necessarily takes place between the outer tube and the bore hole wall. Should the bore hole collapse, the return flow of the driving and rinsing medium is interrupted so that the hammer is put out of opertion.
An object of the present invention is to provide an annular drilling hammer which may be used for continuous drilling without the risk of clogging the discharge of the driving and rinsing medium, thus ensuring a continuous feed of the bored material.